1. Field of the Invention
The present invention relates to systems for feeding solutions to patients. More particularly, the present invention relates to a system and method for monitoring fluid pressures to ensure that the solution is properly fed to the patient by the enteral feeding pump or similar device. Specifically, the invention relates to the use of optical pressure sensors to monitor fluid pressures and the presence of occlusions in the delivery set which may interfere with solution flow to the patient, and so that operation of the enteral feeding pump may be modified to compensate for the pressure and/or occlusion and thereby provide highly accurate solution delivery.
2. State of the Art
There are numerous situations in which a solution must be fed to a patient over a period of time. In some situations, the solution is provided directly into the blood stream of the patient. Saline solutions and medications supplied in such a manner are typically referred to as parenteral solutions. Because parenteral solutions are often necessary to hydrate the patient, or supply needed medications, occlusion of the infusion delivery set can be particularly dangerous to the patient. Thus, it is important to ensure that occlusions are not impeding solution flow. However, parenteral solutions typically have a very low viscosity in order to faciliate absorption into the blood stream. Therefore, the risk of occlusion of the infusion set is relatively small so long as the tube is not pinched shut by folding or some other external application of force.
In contrast to a parenteral system, an enteral feeding system is used to provide nutrient solutions to patients who, for one reason or an other, are unable to eat for themselves. Such a system typically includes a pump which is attached to an input tube connected to a supply container and to an output tube which is connected to a patient. The pump draws nutrient solution from the supply container and delivers the solution to the patient. By adjusting the number of rotations of the motor, or the frequency of rotations, in the pump, an enteral feeding pump can adjust its output to deliver a predetermined amount of nutrient solution (or even medication) at a desired rate.
A significant problem with currently available enteral feeding systems, is that the intake and output tubes may become occluded. Unlike parenteral solutions, enteral feeding solutions have a relatively high viscosity, as they must carry sufficient nutrition to sustain the patient. Occlusion can occur, for example, if a fibrous substance is included in the enteral feeding solution and somehow combines to interfere with flow through the tube. Occlusion can also occur if a tube is bent sufficiently to interfere with flow therethrough, or if a roller clamp (as is commonly used for intravenous applications) is not sufficiently opened. Because of the viscosity of the solution, the amount of kinking of the tube or other interference required to interfere with solution flow is significantly less than that required in a parenteral infusion set.
If the intake tube becomes occluded, insufficient solution may be supplied to the pump, and thus to the patient. If the output tube becomes occluded, the flow of solution may be blocked, or the solution may be suddenly delivered at unusually high pressures. Additionally, medical personnel may fail to notice that the supply container is out of solution, or may not properly mount the intake and/or output tubes in the pump, thereby preventing the proper amount of solution from being delivered to the patient. Any of these scenarios can have tragic consequences if allowed to continue for a prolonged period of time.
Yet another concern with enteral feeding systems is that of viscosity of the solution and viscosity changes as a container full of solution is pumped to a patient. Knowing the viscosity of the fluid being pumped through the enteral feeding system is important because different viscosities are pumped at different rates by the enteral feeding pump. For example, a lower quantity of a highly viscous solution will be pumped by a given number of rotations of the enteral feeding pump motor than will be moved by the same pump when the solution has low viscosity. In other words, the amount of solution fed to the patient can differ substantially depending on the solution""s viscosity. Thus, unless the pump is able to accurately determine and compensate for viscosity changes in the solution (i.e. by increasing or decreasing the rotations of the pump rotor in a given period of time), it is difficult to know exactly how much of the solution has been fed to the patient.
To overcome these concerns, there is a need for a system and method for determining flow discrepancies due to occlusions, viscosity (including changing viscosity) and/or improper fitting of pumps and intake/output tubes so that patients will not be endangered, and so that the proper amount of fluid will be delivered to the patient.
U.S. Pat. No. 5,720,721 (Feb. 24, 1998), which is expressly incorporated herein, provides a significant improvement in monitoring for enteral feeding pumps. The invention uses two pressure sensors to monitor viscosity and occlusions, and to enable the enteral feeding pump to compensate for the varying amount of solution which will pass through the pump with each rotation of the rotor. The pressure sensors engage the elastic tube of the infusion set and monitor changes in the strain on the infusion set by occlusions and viscosity changes. The strain information can then be processed by the pump and adjustments made to the number of rotations of the pump rotor to compensate. In the event that the occlusion is too severe to compensate by modification of the rotor rotations, the pump is shut down and an alarm signal generated so that replacement tubing may be provided.
While the pressure sensor system of U.S. Pat. No. 5,720,721 is a significant improvement over the art, it does have limitations. The pressure sensors described in the ""721 patent are relatively expensive and must be properly mounted in the pump. Additionally, the person loading the pump must make sure that the upstream and downstream portions of the infusion set are properly loaded in the pump housing so that they engage the pressure sensors in the proper manner. Failure to properly load the infusion set can interfere with the functioning of the pressure sensors.
One manner for decreasing the costs of pressure sensors is to use optical sensors. While there are several methods for using optical sensors to determine the presence of occlusions, each has significant drawbacks. Some methods only allow the mechanism to determine when the pressure exceeds a certain threshold. This is done by detecting when the expanding tube of the infusion set engages a surface, thereby modifying reflection or refraction of light. Other methods require complex calculations of refraction indexes or otherwise provide relatively limited information on small pressure changes. Additionally, some methods can vary based on the material from which the infusion set is formed, or based on whether the tube of the infusion set is opaque or transparent.
In addition to the above, many mechanisms for monitoring pressure within an infusion set lack an inherent failure detector. For example, if a sensor is configured to sense only when the expanding infusion set tube engages a transparent surface, the failure to record a reflected signal may mean that the tube has not expanded. In certain situations, however, the lack of reflected signal could also mean that the sensor has failed and is either not sending the signal or is not receiving the reflected signal.
Thus, there is a need for an improved optical pressure monitoring system and method of use. Such an optical pressure monitoring system should be relatively inexpensive and easy to use. It should also provide highly accurate determination of pressure changes which indicate occlusions and/or viscosity changes. Furthermore, it should enable the use of infusion sets made from a variety of materials and without regard to whether the infusion set is formed of a tube which is transparent or opaque.
Thus, it is an object of the present invention to provide an improved method for monitoring viscosity and/or occlusions in an infusion set.
It is another object of the present invention to provide such a method which monitors viscosity and occlusions with an optical sensor system.
It is another object of the present invention to provide such a method in which the material used to form the infusion set does not interfere with proper pressure monitoring.
It is yet another object of the present invention to provide such a method in which the transparency or opaqueness of the solution does not interfere with proper pressure monitoring.
It is still another object of the present invention to provide an optical pressure sensor system with enhanced sensitivity.
It is still another object of the present invention to provide such a sensor system which checks the integrity of the sensor and which ensures that the infusion set is properly loaded in the sensor system.
The various objects set forth above and other objects of the invention are realized in specific illustrated embodiments of a optical pressure monitoring sensor system for monitoring occlusions and viscosity. It will be appreciated that all embodiments set forth may not accomplish all objects of the invention, but that preferred embodiments will accomplish a number of the objects and thereby provide an improvement over the prior art discussed above.
The optical pressure monitoring system typically includes at least one optical pressure sensor having an optical signal emitter and an optical signal receiver. (As used herein, it should be understood that the optical signal emitter is intended to cover electromagnetic radiation, regardless of whether it falls within the range visible to the human eye.) The optical signal transmitter and the optical signal receiver are generally placed on opposing sides of the tube of the infusion set. As the tube expands and contracts due to increases or decreases in pressure, the amount of light (or radiation) received by the optical signal receiver increases or decreases at a known ratioxe2x80x94thereby indicating the pressure within the infusion set.
In accordance with another aspect of the present invention, the tube of the infusion set is positioned between the optical signal emitter and the optical signal receiver so that it will always partially obstruct light flow between the emitter and the receiver. In such a configuration, the optical sensor ensures the infusion set has been loaded properly. If the infusion set is not properly positioned, a greater amount of light will be received by the optical signal receiver. The sensor system can then generate an alarm that the infusion set is not properly loaded in the pump.
In accordance with another aspect of the present invention, the tube of the infusion set is positioned between the optical signal emitter and the optical signal receiver so that the tube will not completely occlude light from the optical signal emitter from being received by the optical signal receiver when the solution within the tube is within acceptable operating ranges. In such a configuration, the sensor system is able to conduct a continuous integrity check. If the optical signal receiver has stopped indicating receipt of light, the lack of a signal will indicate that there has been a sensor system failure and the sensor should be replaced. The failure may be either due to a faulty optical signal emitter which is not emitting the optical signal, or a faulty optical signal receiver which is not detecting the signal sent. Either way, the patient is promptly informed of the failure and can have the sensor replaced.
In the alternative, if the infusion set is positioned to allow complete occlusion of light when the pressure in the infusion set exceeds an acceptable threshold, the alarm signal can be used to signal an occlusion which must be dealt with promptly. If light is still not being received once the infusion set has been removed from the sensor, the patient or technician will know that the sensor is not working and must be repaired or replaced.
Between the two extremes of receiving a full optical signal and no optical signal, the signals generated by the optical signal receiver indicate the extent to which the optical signal sent by the optical signal emitter have been obstructed by the tube. The enteral feeding pump, etc., can convert the measured obstruction into a determination of the pressure within the enteral feeding pump, and the tubing of the infusion set expands in a known proportion to pressure increases. The pressure calculations received can then be converted into information regarding the presence of occlusions and the viscosity of fluid within the infusion set.
With the presence of occlusions and the viscosity of fluid within the infusion set determined, the rotations of the pump may be altered (i.e. increased or decreased) to ensure that the desired amount of solution is infused to the patient. If the pressures detected are outside of acceptable ranges, the pump can be shut down and a signal generated indicating a need to replace the infusion set.
While the monitoring of the tube diameter described above provides improvements over the prior art, it has been found that yet additional improvements in sensitivity can be achieved. In accordance with one aspect of the present invention, a portion of the infusion set tube is made with a thin-walled portion. The thin-walled portion exaggerates tube expansion and contraction due to increases and decreases in pressure. The exaggerated expansions and contractions exaggerate the effect on obstruction of the light transmitted between the optical signal emitter and the optical signal receiver, thereby providing increased sensitivity to changes in the pressure within the infusion set. The voltage change which is caused by the change in light obstruction can, in turn, be converted into more detailed information regarding occlusions and viscosity within the infusion set.
In accordance with another aspect of the invention, a portion of the infusion set is disposed within a jacket. The jacket has an opening on one side through which the tube of the infusion set is visible. On the opposing side of the tube of the infusion set, the jacket is generally solid and restricts the expansion of the tube. As the pressure in the infusion set increases, the expansion of the tube within the jacket is exaggerated at the opening in the jacket because of the restriction caused by the rest of the jacket. This exaggerated expansion increases the sensitivity of readings obtained by the sensor, as the obstruction of light transmission between the emitter and the receiver is enhanced due to the increased movement in the tube wall.
In accordance with another aspect of the present invention the tube of the infusion set is disposed in a generally planar orientation. A portion of the tube is deflected out of the planar orientation by a projection. The projection is typically disposed on a side of the infusion set opposite from the portion of the wall disposed between the optical signal emitter and the optical signal receiver. The projection causes an exaggeration in the expansion and/or contraction of the side of the tube of the infusion set disposed between the optical signal emitter and the optical signal receiver, thereby rendering the sensor more sensitive to pressure changes. Further enhancements in sensitivity can be obtained by controlling the configuration of the projection and the manner in which the projection engages the tube of the infusion set.